LTW3/data/minecraft/loot_tables/gameplay/fishing/fish.json

{
  "type": "minecraft:fishing",
  "pools": [
    {
      "rolls": 1.0,
      "entries": [
        {
          "type": "minecraft:item",
          "weight": 50,
          "name": "minecraft:cod"
        },
        {
          "type": "minecraft:item",
          "weight": 30,
          "name": "minecraft:salmon"
        },
        {
          "type": "minecraft:item",
          "weight": 20,
          "name": "minecraft:pufferfish"
        }
      ]
    }
  ]
}